Alarm cable

ABSTRACT

Alarm cable II, wherein a siren is triggered when there is a loss of mains voltage, characterized in that a switch function (SW) in the connector ( 3 ) also registers that the alarm is not disconnected from the appliance that is to be secured. In the connector ( 3 ) there is also a fastening device ( 14, 15 ) which is connected to a circuit ( 8 ) which registers whether the fastener is released, and then triggers the alarm. In the plug ( 2 ) to the mains supply there is a microswitch (SW) which makes it possible to distinguish between attempted theft and regular power failure. A varistor and a gas discharger connected in parallel relation across the mains phase protect against lightning or surge voltage. There may be input terminals for telephone lines which allow pager or mobile phone signalling.

CROSS REFERENCE TO RELATED APPLICATION

This is the 35 USC 371 national stage of international applicationPCT/NO99/00113 filed on Apr. 6, 1999, which designated the United Statesof America.

FIELD OF THE INVENTION

The invention relates to an alarm cable capable of being installedbetween electrical appliances and one or more power or data signalsources, thereby securing the appliance against theft in addition tofunctioning as a power or data signal supply cable.

With an alarm cable according to the invention, it is ensured that analarm signal is triggered when an attempt is made to disconnect thealarm cable from the power or data signal source or the equipment thatis to be secured. This will complicate the execution of a theft.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,418,521 teaches an alarm cable which, apart from theregular conductors for mains current (and earth), also comprises twoconductors which form part of a current loop around the alarm cable plugto the mains socket outlet, wherein positioned within the plug is aswitch for closing or opening the current loop upon disconnection fromor connection to the mains socket outlet. The switch is embedded in theplug, but can nevertheless be actuated via an arm on connection to ordisconnection from the mains supply.

U.S. Pat. No. 5,418,521 has no facility for discriminating between analarm signal in the event of an actual attempted theft and an alarmsignal in the event of an ordinary loss of supply voltage, inasmuch asit detects changes of state of the switching loop in the same loop as itdetects supply voltage presence.

Furthermore, the alarm cable in the U.S. patent is not capable oftriggering an alarm when the alarm cable is disconnected from theequipment that is to be secured if an unauthorised person first peelsoff the insulation around the cable, and connects an external loop inthe switching loop between the alarm electronics box and the connectorat the end of the cable.

Another weakness of the U.S. patent is that the “alarm box” is locatedat a point along the cable between the connectors at the two ends of thecable, which means that the acoustic alarm signalling unit is easilyaccessible to unauthorised persons who can deaden the alarm sound in anumber of ways, e.g., by lowering the whole “alarm box” into a containerfull of water.

A further weakness with the U.S. patent is that the alarm circuit is notconnected to any locking function for the cable to the equipment that isto be secured. This means that an unauthorised person can disconnect thealarm cable from the equipment that is to be secured, and leave thealarm behind whilst disappearing with the equipment that is to besecured.

SUMMARY OF THE INVENTION

Referring to FIGS. 1a, 1 b, 2, 3, 4 and 5, it is therefore an object ofthe invention to provide an alarm cable which includes at least twoconnector devices selected from a number of different types ofconnector, wherein each connector device includes an electric switch,which switch forms an electric switching loop which is closed when theconnector device is brought together with a female connector and isopened when the connector device is moved from a female connector, atleast one alarm signalling device, and at least one electricallyconducting wire of the multi-conductor type to form electricalconnections between the connector devices of the alarm cable, wherein atleast one connector device is connected to the conductors in a wire,whereof two conductors at the first end area of the wire are connectedelectrically to their respective sides of the switching loop to form acurrent loop, characterised in that at least one connector device alsoincludes a loop detector having a plurality of inputs connectedrespectively to the respective switching loop of the connector and totwo current loop conductors of the connecting wires at the other endarea of the wires, which loop detector supplies a signal when there is achange in one or more of the electrical properties of the current loopor when there is a change of state in the aforementioned respectiveswitching loop, a voltage detector, which voltage detector detects thepresence of an electric voltage supplied from an external electric powersource through one or more connector devices and which gives a signalupon loss of voltage, a control circuit connected to the loop detectorand the voltage detector, which control circuit sends a control signalof limited duration in response to the presence of a signal from thevoltage detector only, which control circuit sends a prolonged controlsignal in response to the presence of signals from the loop detectoronly or on the concurrent presence of signals from both the loopdetector and the voltage detector, and an alarm signalling device whichreceives the aforementioned control signals and which gives at least onealarm signal in response to the presence of control signals.

Protection of equipment is achieved according to the invention in thatan alarm cable is plugged into the power or data signal input terminalin the equipment that is to be secured, and to a power or data signalsource, such as the mains supply. Voltage from the power or data signalsource is detected by a voltage detector. Furthermore, there runs from acontrol circuit a current loop via switches in the alarm cableconnectors, which is opened or closed upon disconnection from orconnection to the equipment that is to be secured and also the power ordata signal source. A similar current loop at the loop detector ofresistor elements in the cable connectors detects any changes of statein the electrical properties of the loop, and gives an alarm on“unauthorised connection” of the loop along the cable between theconnectors. In another current loop a fixing pin(screw) and (a washerat) the fastening piece are connected in series, so that via the controlcircuit a prolonged alarm signal is given when changes in the electricalproperties of the loop occur upon unauthorised manoeuvring of the fixingpin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1 b, 2, 3, 4 and 5 depict an alarm cable according to theinvention for installation between the mains outlet socket and the powerinput terminal of the appliance that is to be secured; and

FIGS. 6a, 6 b and 6 c are schematic illustrations of electronic circuitsfor an embodiment according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, seen in conjunction with FIGS. 1a, 1 b, 3, 4 and 5,an example of a preferred embodiment of the alarm cable according to theinvention is described below. The same reference numerals indicate thesame elements. The embodiment describes an alarm cable for installationbetween the mains outlet socket and the power input terminal of theappliance that is to be secured.

The alarm cable is supplied with current from the 230V mains supply 9via transformer TRA and from a separate floating battery. Thetransformer TRA is located in the plug 2 of the cable together withassociated rectifier and smoothing capacitor. The transformer inlet isprotected against surges by means of a varistor. The battery and avoltage regulator are located in the appliance part 3 of the cable.Battery maintenance and conditioning are controlled by a microcontrollerwhich functions as control circuit 11.

A separate voltage detector 10 detects whether a 230V mains supply ispresent by measuring whether the transformer provides sufficiently highvoltage. When voltage is unduly low, a message is given tomicrocontroller 11.

A common switching loop 7 detects whether a microswitch SW in theconnector part 2 or a microswitch SW in the appliance part 3 is trippedbecause the cable is unplugged. Detection is effected by measuringwhether a series resistance R of normally 1 kΩ is present or whether itis changed substantially (e.g., by a short circuit to 0V or by breaks inthe cable at 4, 6) by comparison with known values.

The alarm cable 1 makes use of a plurality of connections for currentloops 7 and switching loops 5. Breaks in one or more of these will bedetected.

Loop breaks are detected by separate components which together form theloop detector 8, and status of the loops is monitored by microcontroller11.

Six switches constitute the keypad. These are read directly by themicrocontroller 11 and function as an input point for key codes whichcontrol the activation or deactivation 13 of alarm functions.

The alarm relaying unit 12 includes a separate acoustic alarm member forwarning of alarms on direct control of microcontroller 11.

The control circuit 11 in this embodiment consists of a microcontrollercircuit from Atmel, AT90S1200.

Alarm cable II according to the invention is shown in FIG. 2, which is aview of the alarm cable II from above, wherein: 3 is the connector, withthe fastening piece 4; 8, 10, 11 and 12 constitute the alarmelectronics; 4 is the wire between the connector 3 and the plug 2; 2 isthe plug to the mains supply; SW is a microswitch in the plug 2. Oninstallation, the connector 3 is inserted into the input terminal of theappliance that is to be secured, and after current connection alarmcable II is activated using the keypad.

FIGS. 6a, 6 b and 6 c are schematic illustrations of electronic circuitsfor the embodiment described above which include a loop detector, avoltage detector, a control circuit, a signal alarm relaying device withacoustic transducer, power supply and battery with battery controlcircuit.

In FIG. 6a microcontroller U100, together with the resistors R100, R101and R102, constitutes primarily control circuit 11 and loop detector 8,whilst SP100, T190 and R100 constitute the actual alarm signaler 12, andS100-S105 form the key input keypad for activating or deactivating 13.The switch S100 indicates switching loop 5 in the connector with controlelectronics.

FIG. 6b shows battery B150 together with the battery control circuitactive components Q150 and Q151, and electronics U150 and D151 forvoltage monitoring and detection 10.

FIG. 6c shows electronics power supply with 220V input, with steppingdown by the transformer T200 and rectifying by D200A, D201A, D200B andD201B.

What is claimed is:
 1. An alarm cable (1) including at least twoelectric connector devices (2, 3) selected from a number of differenttypes of connector wherein each connector device includes an electricswitch SW, which switch forms an electric switching loop (5) which isclosed when the connector device is brought together with a femaleconnector and is opened when the connector device is moved from a femaleconnector, at least one alarm signalling device, and at least oneelectrically conducting wire (4) of the multi-conductor type to formelectric connections between the alarm cable connector devices, whereinat least one connector device is connected to the conductors of a wire,whereof two conductors (6) at the first end area of the wire areconnected electrically to each side of the respective switching loop ofthe connector device to form a current loop (7), characterised in thatat least one connector device further comprises a loop detector (8)having a plurality of inputs connected respectively to the respectiveswitching loop of the connector and to two current loop conductors ofthe connecting wires at the other end area of the wires, which loopdetector gives a signal when a change in one or more of the electricalproperties of the current loops occurs or when there is a change ofstate in the aforementioned respective switching loop; a voltagedetector (10), which voltage detector detects the presence of anelectric voltage supplied from an external electric power source (9)through one or more connector devices and which gives a signal whenthere is a loss of voltage; a control circuit (11) connected to the loopdetector (8) and the voltage detector (10), which control circuit givesa control signal of limited duration in response to the presence of asignal from the voltage detector only, which control circuit gives aprolonged control signal in response to the presence of a signal fromthe loop detector only, or on the concurrent presence of signals fromboth the loop detector and the voltage detector; and an alarm signallingdevice (12) which receives the aforementioned control signals and givesat least one alarm signal in response to the presence of a controlsignal.
 2. An alarm cable as disclosed in claim 1, characterised in thatthe alarm signalling device also includes means for transmission ofalarm signals to remote alarm relaying equipment.
 3. An alarm cable asdisclosed in claim 1, characterised in that the alarm device alsoincludes means for giving audible or visible warning signals.
 4. Analarm cable as disclosed in claim 1, characterised in that in one ormore switching loops (5) there is inserted an electric resistor element(R) electrically connected in series with respective switches.
 5. Analarm cable as disclosed in claim 1, characterised in that it alsoincludes a fastening device (14) provided with a release catch (15)having switching loop function, wherein the switching loop of thefastening device is opened by operating a fastening device releasecatch, the switching loop of the fastening device being connected to theloop detector (8).
 6. An alarm cable as disclosed in claim 1,characterised in that it also includes an activation/deactivation device(13) with key control, which device is connected to the control circuit(11) for selective activation and deactivation of alarm functions.
 7. Analarm cable as disclosed in claim 1, characterised in that the currentloops and switching loops are connected in electric series connection.8. An alarm cable as disclosed in claim 1, characterised in that atleast one connector device includes electric fusing elements tocounteract overvoltage supplied from at last one external electric powersource.
 9. An alarm cable as disclosed in claim 8, characterised in thatat least one external electric power source is selected from a groupconsisting of a regular electricity mains supply, a standing currentgenerator and a data signal source.